The two major defensive peroxidases of the mouth are salivary peroxidase (SPO) and myeloperoxidase (MPO). Their function depends partly on diet and probably also on genes.
In the abstract of the paper, the authors mention that their earlier study showed that elderly people who drank green tea for 3 months had higher levels of oral peroxidase activity than non-drinkers. In this study, they compared the effects of green tea on OPO in vivo and in vitro.

Adding a green tea infusion to saliva increased oral peroxidase activity by 280%, while black tea increased it by only 54%. Adding only epigallocatechin gallate (EGCG), the main polyphenol in green tea, increased activity by 42%. The effect was dose-dependent, which I assume here means that the stronger the tea, the greater the effect.

In human subjects, green tea gave a very similar result. Mouth rinsing with a green tea infusion resulted in a 268% increase in OPO activity. Thus, while green tea extracts may be more useful than just drinking regular green tea for some purposes, for dental health drinking and/or rinsing is probably the most effective way.

Note, however, that higher levels of salivary peroxidase don't necessarily mean better oral health; in fact, people with more dental caries and gingivitis tend to have higher SPO activity (link). My guess is that this is a defense mechanism against the harmful effects of excess hydrogen peroxide, which is excreted by oral bacteria. In other words, the stronger the attack, the stronger the defense.

In the case of green tea it seems that increasing SPO really does lead to better oral health, though.

Thursday, September 13, 2012

Most of the recent documentaries and newspaper pieces on calorie restriction haven't really offered anything new. They pretty much just repeat the same old arguments about mice eating less and living longer, and then joke that starving yourself will at least make your life seem longer.

This recent BBC Horizon documentary was a positive surprise, however. It does a pretty good job of covering both traditional calorie restriction (CR) and various forms of intermittent fasting (IF), and while the scientists are overly optimistic about either strategy extending maximum lifespan in humans, they do make some good points.

There's for example Luigi Fontana, something of a celebrity in the CR research field, who thinks practicioners of calorie restriction are so much healthier than the average person that they almost "belong to another species". Right. The host of the show correctly points out that Joseph Cordell, the decade-long CR practitioner he interviews, doesn't look remarkably younger than the average 50-year-old.

His blood tests do indicate a very good health, however, and what's interesting is that Cordell is not severely calorie-restricted – he eats 1,900 kcal per day. For an average male, I think that's entirely doable, as long as you pay attention to the nutritional value of the diet to avoid hunger. Cordell also doesn't have that "cancer patient" look to him that a lot of CR skeptics worry about; he's thin but not overly so.

Several of the scientists and professors in the documentary seem to think that intermittent fasting is as good as calorie restriction for longevity, even though the evidence shows otherwise: in animals, IF results in increased lifespan only to the degree that it also results in CR. One of the researchers advocates a diet of fasting and feasting every other day, but not in the traditional 24-hour cycles. Instead, she recommends eating around 400-600 kcal on the fast days and as much as you like on the feast days.

In my experience, at least the 24-hour cycle of fasting and feasting (where you're not allowed any calories during the fast) results in eating twice as much during feast days, unless you purposefully count and restrict calories during feast days as well. She says that there is a calorie deficit, however: during fast days, you're allowed around 25% of your normal calorie intake, and during feasting days you naturally end up eating around 110% of your normal intake. This sounds very strange to me, as it would mean an easy way of accomplishing rather severe CR. I am intrigued by this semi-fasting approach, though.

Another form of IF tried in the documentary is alternate-day feeding based on weekdays instead of 24-hour cycles, i.e. you eat on Monday and then don't eat on Tuesday etc. This is much more difficult than IF based on a 24-hour cycle, since you're essentially fasting around 32 hours at a time. Then there's the 5/2 approach, where you eat for 5 days and then fast for 2 days. And the "4 days of fasting every few months" approach. In the IF circles, there's still debate over which approach is best. Last time I looked, nobody knew the answer to how many hours of fasting is needed to produce the best benefits in humans.

A point that keeps coming up in the documentary is the effect of IGF-1 on aging and the effect of fasting and/or calorie restriction on IGF-1. As Fontana's research suggests, lowering IGF-1 may be crucial for any lifespan extension effects of CR. The 4-day fast clearly lowers IGF-1, but the effect doesn't last long. Cordell's IGF-1 levels are not shown, but since his blood parameters are those of a young man, I assume his IGF-1 is lower than average; probably due to a combination of slight CR and protein restriction.

If you ignore the unrealistic expectations of extending maximum lifespan in humans, the results are overall pretty optimistic. It seems that even a slight reduction in calories and fasting every now and then might significantly improve your health parameters.

Put another way, IF and CR might not make humans live to 120, but they might make you live to 100 without dying of the usual killers like cancer and heart disease. I haven't heard of Joseph Cordell before and am not familiar with how all of his biomarkers look like, but if it is true that he eats 1,900 kcal per day and has only been doing CR since his 40's, perhaps I've underestimated some of the potential benefits of eating only slightly less. Personally, I haven't been doing intermittent fasting for a couple of years now, but I guess it's time to read up on the latest studies and see what's happening out there.

For more information on calorie restriction and intermittent fasting, see these posts:

Wednesday, August 8, 2012

Avocados contain plenty of MUFAs, most of which is oleic acid. (Photo by Muffet)

Everyone knows avocados are high in fat, but does that make them healthy or unhealthy? In this post, we'll look at how avocados affect cholesterol levels.

Avocados are technically large berries of the avocado tree, each berry containing a single seed usually called the avocado stone. There are several different cultivars, but on average avocados contain about 15 grams of fat, 9 grams of carbohydrates and 2 grams of protein per 100 grams. Most of the fat (~10 grams) is monounsaturated, while the rest is roughly half saturated and half polyunsaturated.

Most health enthusiasts are either pro-saturated fatty acids (SAs) or pro-polyunsatured fatty acids (PUFAs) – and if you're a long-time reader of this blog, you already know which category I lean towards. Monounsatured fatty acids (MUFAs), however, seem to represent something of a "neutral" group of fats to many. Olive oil, for example, is high in MUFAs, and almost all studies find it either beneficial or at least neutral: generally, LDL decreases and HDL either increases or stays the same.

So if olive oil is good for you, what about avocados? Since both are high in MUFAs, specifically oleic acid, one might expect to see similar results. In rats, adding avocados to their diet seems to increase HDL and decrease triglycerides (link). Avocado leaf extracts appear to be especially effective (link).

Avocados, cholesterol & healthy subjects

Experiments on humans, unfortunately, are not always as unequivocal. The earliest human study I could find compared an avocado-enriched diet with a diet high in complex carbohydrates and low in fat – namely, the lipid-lowering diet advocated by the American Heart Association (link). The study included 15 women who were randomly assigned to one of the diets for three weeks, followed by 3 weeks on the other diet. Only the avocado diet, on which the women ate between half and one and a half avocados per day, resulted in a statistically significant decrease (~8%) in total cholesterol levels. This was due to a lowering of LDL without affecting HDL, whereas the complex carbohydrate diet lowered HDL levels by ~14%. So much for the heart-healthy effects of low-fat diets.

The second study included 16 healthy volunteers who were fed three different diets for 2 weeks: a high-MUFA diet consisting of 30% fat (75% of which came from avocados), a free diet including avocados, and a low-saturated fat without avocados (link). Both the high-MUFA diet and the low-SA diet reduced total cholesterol and LDL. However, the low-SA diet also also reduced HDL and increased triglycerides, while the other two diets reduced triglycerides. Again, the low-fat diet with an emphasis on limiting saturated fats was the most harmful for cholesterol levels.

I find it somewhat surprising that the free diet with avocados apparently also reduced HDL, even though the authors say the volunteers ate the same amount of avocados as during the high-MUFA diet. Unfortunately I don't have access to the full paper, so I'm not sure what the free diets were like in reality. Perhaps the volunteers simply ate more during the free diet, which could have skewed the results, or maybe the SA/PUFA ratio was significantly lower on the free diet for some reason.

Avocados and people with high cholesterol

Another study included 13 patients with high LDL cholesterol (link). The patients were given a standard vegetarian diet, a vegetarian diet enriched with avocado or a free diet that included avocados. The standard vegetarian diet consisted of 70% carbs, 20% fat and 10% protein, while the vegetarian avocado diet was 60% carbs, 30% fat and 10% protein. The vegetarian avocado diet reduced LDL, whereas the free diet increased it slightly. Only the standard vegetarian diet significantly reduced triglycerides – however, it also reduced HDL more than the other two.

The results of this study seem to contradict the two earlier studies, since simply adding avocados to the diet resulted in slightly lower HDL and slightly higher LDL – in other words, their cholesterol levels worsened. Genetics may play a role here, as some individuals who are predisposed to higher LDL levels seem to react negatively to foods that generally improve the cholesterol ratio. The authors themselves state:

"Low-fat, carbohydrate-rich vegetarian diets may be harmful to hypercholesterolemic patients. The avocado addition to a vegetarian diet does not correct these undesirable effects. To obtain beneficial effects on lipid profile with avocado, lower amounts of carbohydrates and polyunsaturated fatty acids are probably needed."

Yet another study compared the effect of an avocado-enriched diet on healthy subjects and patients with slightly elevated cholesterol levels (link). In healthy participants, total cholesterol decreased by 16% on the avocado diet. In participants with high cholesterol, total cholesterol decreased similarly, with LDL and triglycerides decreasing by 22% and HDL increasing by 11%. The authors conclude that a high-MUFA diet containing avocados improves lipid profile in healthy and especially in mildly hypercholesterolemic people.

Conclusion

Compared to low-fat diets, diets containing moderate to high amounts of monounsaturated fatty acids from avocados seem to result in better cholesterol levels. In healthy people, replacing carbohydrates with avocados generally lowers LDL without affecting HDL, similar to olive oil. In people with high cholesterol, replacing carbohydrates with avocados appears to reduce LDL and, in some cases, increase HDL.

The controversial result is the lower HDL in free diets with avocados. Does simply adding an avocado to your diet actually make cholesterol levels worse? This is a tricky question, since adding an avocado would mean an increase in total energy intake, unless it also means you eat less of something else – which would be the case, unless avocados somehow increase appetite. One possibility is that when the participants added avocados (and thus MUFAs) to their diet, they reduced their consumption of other fatty acids while keeping total energy intake the same. Reducing saturated fatty acid intake could result in lower HDL, although this doesn't necessarily explain the higher LDL. Without knowing what the participants actually ate during their free diet periods, it's difficult to say what the cause is.

While it's generally taken for granted that a) olive oil reduces LDL and has a neutral or positive effect on HDL and b) this effect is due to the high MUFA content of olive oil, there are differences in the food sources of MUFAs. Both avocados and olive oil are high in oleic acid, but olive oil contains squalene, whereas avocados do not. Squalene is a precursor in cholesterol synthesis and is metabolized to cholesterol in the body. Avocados, on the other hand, contain beta-sitosterol, which lowers LDL.

Finally, genes play a major role in cholesterol levels. Apolipoprotein E genotype affects how individuals react to dietary fatty acids and also cholesterol-lowering drugs like statins. Without knowing the genotypes of the participants in the studies, it's hard to say how generalizable the results are.